Immunopathogenic studies were performed on patients with a diversity of immune mediated diseases. An isolated defect in NK cell activity was described in patients with the Chediak-Higashi syndrome constituting the first description of a primary human immunodeficiency disease with an isolated defect in NK cells. This selective defect was corrected in vitro by inducers of cAMP thus providing a basis for potential correction of this defect in vivo. Patients with the Kaposi sarcoma-opportunistic infection syndrome seen predominantly among male homosexuals were studied. A profound and selective defect in the T4 inducer subset of T cells was demonstrated together with a defect in the ability to respond in vivo and in vitro to T cell dependent B cell stimulation despite the presence of hypergammaglobulinemia in vivo. A large number of patients with the idiopathic hypereosinophilic syndrome (HES) were studied. Mechanisms of organ system damage and dysfunction were delineated predominantly with regard to the role of the eosinophil in the endocardial damage characteristic of HES. Mechanisms of aberrant B cell activation and immunoregulation were delineated in several autoimmune diseases of both the organ specific (Hashimoto's thyroiditis) as well as the organ non-specific (systemic lupus erythematosus and Sjogren's syndrome) type.